1. Technical Field
The present invention relates generally to a light-distributing lens of a head lamp for use in vehicles, and more particularly to a light-distributing lens designed to emit light transmitted through an optical fiber to form a high intensity light zone and a wide spread light zone ahead of the vehicle.
2. Background of Related Art
U.S. Pat. No. 5,499,166 issued on Mar. 12, 1996 to Kato et al., assigned to the same assignee as that of this application discloses a lighting device having a high intensity zone-forming lens and a wide spread zone-forming lens, which will be discussed below using the same reference numbers as employed in the above publication.
The wide spread zone-forming lens includes an entrance surface 26c, a pair of right and left reflecting surfaces, and two exit surfaces 26a and 26b. The light emerging from an optical fiber 30 enters the entrance surface 26c. The right and left reflecting surfaces direct the light transmitted from the entrance surface 26c forward in total reflection. The exit surfaces 26a and 26b emit part of the light emerging from the entrance surface 26c or direct light which has not undergone total reflection on the reflecting surfaces and the remainder of light which has undergone the total reflection on the reflecting surfaces in forward directions, respectively, to form a smaller light-distributed area C1 and a larger light-distributed area C2 (see FIG. 4(B) of the publication). The smaller light-distributed area C1 is defined by a direct light-distributed portion formed by the direct light emerging from the exit surface 26a and right and left reflected light-distributed portions formed at the right and left sides of the direct light-distributed portion by the reflected light emitted from the reflecting surface 26a. The larger light-distributed area C2 is defined by a direct light-distributed portion formed by the remainder of the direct light emerging from the exit surface 26b and the remainder of the reflected light emitted from the reflecting surface 26b.
The above prior art lens structure, however, has the following drawbacks.
The pair of right and left reflecting surfaces are common to the exit surfaces 26a and 26b. Specifically, the angle at which the right and left reflecting surfaces expand forward is unchanged in the exit surfaces 26a and 26b, so that image pitches (i.e., intervals) between the direct light-distributed portion and the right and left reflected light-distributed portions formed by the light emitted from the exit surface 26a are substantially equal to those between the direct light-distributed portion and the right and left reflected light-distributed portions formed by the light emitted from the exit surface 26b. This produces dark areas outside and between the direct light-distributed portion and the right and left reflected light-distributed portions formed by the light emitted from the exit surface 26a which overlaps with only part of the light-distributed area formed by the light emitted from the exit surface 26. Therefore, only certain parts of the dark areas are brightened by the light emitted from the exit surface 26b, resulting in uneven distribution of brightness of the light-distributed areas formed by the wide spread zone-forming lens.